Insulin-like hormones known as bombyxins have been found in a variety of insect species yet their functions remain largely undefined. In vertebrates, insulin receptors are members of the growth factor family of receptors, i.e., proteins with intrinsic tyrosine kinase activity which are autophosphorylated upon activation. Hence, we hypothesized that insect insulin-like hormones would stimulate tyrosine phosphorylation of membrane-associated insect proteins. We have found that a protein similar to the insulin receptor is present in Manduca sexta, co-precipitable with tyrosine kinase activity, associated with a glycoprotein, cross-reactive with antibodies directed against the human insulin receptor, and tyrosine-phosphorylated in response to insulin-like hormones and an endogenous factor present in Manduca brain. We have recently isolated a fragment of an insulin receptor cDNA with 65-75 percent homology to the receptor found in vertebrates and Drosophila melanogaster. Specific objectives of the current proposal are a natural extension of these results: 1) isolation and expression of a full-length cDNA clone for the Manduca insulin receptor; characterization of mature receptor size and ligand-stimulated kinase activity; 2) investigation of the sites and times during development when the receptor is maximally transcribed, using Northern blotting, RT- PCR, and in situ hybridization; 3) isolation and expression of cDNA for endogenous ligand(s) based on homology with known bombyxins, or alternatively, by isolation from partially purified neural extracts using expressed receptor as an affinity reagent; and 4) initial exploration of functional changes in insect cells elicited by endogenous, or active exogenous, ligands for the insulin receptor. The proposed work develops essential tools with which to conduct future experiments on the functions and intracellular modes of action of the insulin receptor in specific lepidopteran target tissues. Such work will further basic understanding of the early insulin receptor, and be potentially applicable to the development of novel insect control agents.